Like all classic running films, there will be "lovely artistic sunset runs" but also "the nitty-gritty" that Rai has had to negotiate.

Belcher, 42, grew up in Hong Kong and has spent most of his life here, with stints in Cyprus, Germany and Britain. The former lecturer in criminology at the University of Hong Kong is a trail-running fanatic and first met Rai last year, when she came to Hong Kong to compete in the MSIG Lantau 50 ultramarathon. After taking her promotional photos, Belcher became fascinated by her story.

"Not just running, but her life story," he says.

Aged 14, Rai left Bhojpur, in eastern Nepal, to join a Maoist camp, and lived with 600 rebels for two years in a bamboo fortress until its members were demobilised.

Rai travelled to Kathmandu, where she started running. In her first 50km ultramarathon race last March, in the Nepali capital, she "totally destroyed everyone", says Belcher. By September, Rai was racing in Europe and taking on renowned runners.

The film, 90 per cent of which is in Nepali with English subtitles, will be released online on December 7. Belcher is working with NGOs to make it available in schools and rural villages across Nepal. The ultimate goal, he says, is to inspire "another generation of sportswomen" in Rai's home nation.